Method and apparatus for increasing uniformity of heat transfer

ABSTRACT

A method and apparatus for increasing the uniformity of heat transfer in a heat exchanger. The flow of the medium which is to be heated is regulated in such a way as to provide a uniform outlet temperature of this medium at the outlet ends of the tubes. This is achieved by throttling the flow of the medium into the inlet ends of the tube. After measuring the temperature of the medium at the outlet ends of the tubes, a throttling at the inlet ends is provided to achieve uniform temperatures at the outlet ends, respectively.

United States Patent METHOD AND APPARATUS FOR INCREASING Inventors PaulViktor Gilli Vienna; Kurt Fritz, Klosterneuburg; Walter Roznovsky,Vienna, Austria Appl. No. 785,491 Filed Dec. 20, 1968 Patented Feb. 16,1971 Assignee Waagner-Biro Aktiengesellschaft Vienna, Austria PriorityJan. 15, 1968 Austria UNIFORMITY OF HEAT TRANSFER 13 Claims, 6 DrawingFigs.

US. Cl 165/1, 165/ 101 Int. Cl F 28f 27/02 [50] Field ofSearch 165/1,39, 40,101,163,l74

[56] References Cited UNITED STATES PATENTS 2,070,427 2/1937 Faunce165/174 3,406,745 10/1968 DeCastelet 165/40 Primary Examiner-CharlesSukalo Attorney-Steinberg and Blake \M lk I2 l6 [IE ,4 s"

PATENIED ram 6&9?!

SHEET 2 0F 3 1' A/ MIN 76/? 5 mm mm? fl/LL WA fE-R jaw R0 NoVsK yATENTEU FEB I 6 I97! SHEET 0F 3 BACKGROUND OF THE INVENTION The presentinvention relates to a method and apparatus for increasing theuniformity of heat transfer in heat exchangers.

in particular, it is an object of the invention toprovide a method andapparatus which will increase the uniformity of operation of a heatexchanger wherein part. of the tubes through which the heated mediumflows are necessarily rendered inoperative. f i

Thus, for example, it sometimes-happens during operation of a heatexchanger that a certain part of the tubes thereof become defective dueto the occurrence of an accident, for example, and the situation isoften one where the location of the defective tube or tubes is such thatit is inaccessible. Under these conditions it becomes necessary toterminate the operation of such defective tubes.

It has already been proposed to terminate this operation by plugging upthe defective tubes so that they will nolonger participate in the heatexchange. Such plugging of the defective tubes necessarily results in adecrease in the extraction of the heat from the heating medium atpredetermined locations. The heat-exchanging operations will now takeplace with a sharp decrease in uniformity with those tubes :in theimmediate vicinity of the plugged defective tubes which are no longerused becoming heated to an extent greater than other tubes. A similareffect can in fact be encountered during starting up operations when thedesign of the system has been carried out in such a way that not enoughcare was taken to achieve, uniform discharge temperatures at theindividual tubes, or in the case where during manufacture of theindividual tubes localized narrowing or reductions in the cross sectionof the path of flow result from. factorssuch as a welding bead which istoolarge and whichis improperly situated so that it extends into andundesirably restricts the path of flow at a localized area. Yet anothersource for a deviation in the structure resulting in nonuniformoperation is the different internal diameters of the heat-exchangingtubes necessarily resulting from conventional manufacturing tolerances.Furthermore, it is not possible to avoid certain deviations from anideal construction in the design of a given system, particularly in thecase of bundles of helical tubes forming part of a system where thehelical tubes define pipe cylinders of different diameters. in an actualconstruction it is essential to provide such a pipe cylinder with agiven whole number of tubes while according to theory,.a fractionalnumber of tubes, rather than a whole number of tubes, will be requiredto achieve uniform operation. Thus, for all of these reasons it isunavoidable that a lack of uniformity will be encountered in theoperations of heat exchangers. Of particular significance, however, isthe case where one or moreindividual tubes must be excluded from theoperations as a result of damage to such tubes with the damaged tubeslocated where they cannot be repaired either because the location of thedamaged tube or tubes is inaccessible, or because of the presence ofradioactivity in the region of the damaged tube or tubes. Thus, incertain through-flow steam generating constructions, which are heatedwith gases, liquids or liquified metals from a nuclear reactor, it iseither not possible to carry out repairs directly in a given bundle oftubes or repairs can only be made after a long waiting time has expired,Such difficulties are also encountered in conventional installations,however, where the tubes of the bundles are packed with a particularlyhigh density. All of these latter effects are encountered to aparticularly large extent in the case of through-flow steam generatorswhich do not have any intermediate collection of the heated fluid.

SUMMARY OF THE INVENTION It is accordingly a primary object of theinvention to provide a method and apparatus which will avoid the abovedrawbacks. a

In particular, it is an object of the invention to provide a method andapparatus which will achieve uniformity in the operation of a heatexchanger even in the case where part of the tubes thereof must beexcluded from the operations.

in particular, it is an object of the invention toprovide a method andapparatus which will result in a substantial increase in the uniformityof the temperature of a heated medium where it discharges from heatingtubes in the case where part of the latter tubes must be excluded fromthe operations.

It is especially an object of the invention to provide a methodaccording to which it is possible to determine how to modify a givenheat-exchanging system so as to achieve uniformity in the operationthereof after a given part of the heating tubes have been damaged so asto require part of the tubes to be rendered inoperative. I p

Also, it is an object of the invention to provide an exceedingly simplestructure which can be added to an existing installation for the purposeof rendering the operation thereof more uniform in the case where it isnecessary to exclude certain tubes from the operation.

In accordance with the invention the heat exchanger has a plurality oftubular means respectively provided with inlet and outlet ends. lnaccordance with the invention the medium which is to be heated isdirected through the plurality of tubular means in such a way that thetemperature of this medium at the outlet ends of the tubular means issubstantially uniform. in accordance with the invention, this result isachieved by throttling the flow of the medium which is to be heated intothe inlet ends of the plurality of tubular means in such a way that thismedium will have a uniform temperature at the outlet ends. Each tubularmeans may take the form of a single tube or a group of tubes. Thethrottling at the inlet ends of the plurality of tubular means isbrought about by a throttling means which preferably takes the formof asuitably apertured plate having throttling apertures which respectivelycommunicate with these inlet ends. in the event thatthere are tubeswhich for any reason no longer operate, then the aperture plate hasthrottling apertures which respectively have such a size that the extentof flow of medium through tubes in the immediate vicinity of those whichno longer operate is greater than the extent of flow through the tubeswhich are more distant from the part of the tubes which have beenrendered inoperative. Temperature measurements are carried out at theindividual outlet ends of the plurality of operating tubular means fordetermining the temperatures at these several outlet ends, respectively,and in accordance with the latter temperatures a given throttling meansis situated at the inlet ends to achieve the uniform temperature at theoutlet ends. Thus, where there are tubes which no longer operate, theapertured throttling plates can have at the inlet ends immediatelyadjacent those tubes which no longer operate throttling apertures whichare greater than more distant throttling apertures either absolutely orwith respect to the latter apertures. Thus, in the case of heat exchangebetween a medium within longitudinally extending tubes and a hot fluidat the exterior of the tubes, the lesser extent of throttling isprovided at those tubes which surround any inoperative tube or tubes. Inthe case where the heating fluid flows transversely across a bundle oftubes through which the heated medium flows, the lesser extent ofthrottling is provided at those tubes situated in the direction of flowof the medium which gives up its heat as well as, to a lesser extent, atthose tubes which are in the immediate vicinity of any damaged tubeswhich no longer operate.

Thus, with the structure of the invention a throttling means is situatedat the inlet ends of the plurality of tubular means to throttle the flowof the heated medium through the plurality of tubular means in a mannerdetermined by the discharge temperatures at the outlet ends of theplurality of tubular means for regulating the flow of the heated mediumthrough the operating tubes to achieve uniform temperatures at theoutlet ends of the tubular means. The throttling means, according to afurther feature of the invention, preferably takes the form of anapertured plate which is situated in front of an inlet plate to whichthe inlet ends of the several tubular means are connected. In order tomeasure the temperature of the medium discharging at the outlet ends ofthe tubular means, a thermocouple means situated in accordance with theinvention at the region of an outlet plate to which these outlet endsare connected, and the thermocouple means is capable of measuring thetemperature of the medium which discharges at the outlet ends of theindividual tubular means.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way ofexample in the accompanying drawings which form part of this applicationand in which:

FIG. I is a partly sectional schematic elevation of a heat exchangerhaving helical heat-exchanging tubes;

FIG. 2 is a schematic sectional elevation of that type of heat exchangerwhere the tubes are respectively arranged in planes to form partitionwalls in the heatexchanger;

FIG. 3 is a fragmentary longitudinal sectional elevation schematicallyillustrating one embodiment of a throttling DESCRIPTION OF PREFERREDEMBODIMENTS Referring to FIG. 1, the heat-exchanger installationillustrated therein includes a plurality of helical tubular meansthrough which the medium to be heated flows. In the illustrated examplethe plurality of tubular means are in the form of individual helicaltubes 5 which define tube cylinders I4. The tube cylinder 1 issurrounded by the tube cylinder 2 which is itself surrounded by the tubecylinder 3, and this latter tube cylinder is, of course, surrounded bythe outer tube cylinder 4. Each of these cylinders is defined by aplurality of helical tubes 5 having convolutions of the same diameter.Thus, the tubes which define the cylinder 1 have convolutions of thesmallest diameter, while the tubes which define the cylinder 4 haveconvolutions of the largest diameter, and of course the cylinders 2 and.3 have tubes of corresponding diameters between those of the cylindersl and 4. Within each cylinder the several tubes which define the sameare connected in parallel and within each cylinder all of the tubeswhich define the same have the same length. Thus, each tube cylinder iscomposed of a given number of parallel-connected helical tubes allofwhich are of equal length.

The heating medium, in the form of a hot gas, enters at the top of theinstallation through the gas inlet 6, and heat is extracted from the hotgas entering through the inlet 6 to generate steam. The heat isextracted from the gas through the walls of the helical tubes 5, and thecooled gas leaves the steam generator at the lower outlet 7 thereof. Theinstallation is situated within the elongated housing 8 which has theinlet 6 at its top end and the outlet 7 at its bottom end.

The number of parallel-connected tubes 5 in the several tube cylindersl--4 is different in the respect 'of cylinders. Thus, at the outercylinder 4 which has the largest diameter there will be moreparallel-connected tubes than in the remaining tube cylinders whichsuccessively have decreasing numbers of tubes from the outer to theinner cylinder 1, the latter of course having the smallest number oftubes. The difference between the numbers of tubes of the severalcylinders is such that the longitudinal pitch of all of the helicaltubes 5 is identical for all of these tubes in the several cylindersl-4.

The feedwater flows from the feedwater inlet I5 into the supply chamberl3where the feedwater is collected. At this chamber 13 the feedwater hasaccess to an inlet plate ll formed with bores which receive the inletends of the plurality of tubular means 5. The throttling means of theinvention is situated in front of this inlet plate 11 and the severaltubular means 5 include, in addition to the helical portions thereof.the tubular extensions 9 respectively communicating with the severalhelical tubes and terminating in the bores of the inlet plate 11 inwhich the inlet ends of the extensions 9 are received in a fluidtightmanner. Thus, through the several extensions 9 of the plurality ofhelical tubular means a communication is made with the feedwaterwhich ispreheated, heated. converted into steam, and superheated within thehelical tubes 5.

The live steam discharges from the plurality of tubular means 5 intotubular extensions 10 respectively communicating with and extending fromthe tubular means 5 and received in bores of an outlet plate 12 wherethe outlet ends of several tubular means are located, these outlet endsbeing defined by the outlet ends of the extensions 10 of the severaltubular means. Thus, the live steam will flow from the helical tubes 5respectively through the extensions 10 thereof and the outlet plate 12,which fluidtightly receives the extensions 10 in bores of the plate 12,respectively, into the live-steam collecting chamber 14, from which thelive steam flows to the conduit 16. The outer cylindrical housing 8 forthe entire installation is capable of withstanding high pressure and issuitable for use with gas at high pressure, particularly with gasissuing from a nuclear reactor.

In the type of heat exchanger which is illustrated in FIG. 2, theseveral tubular means are respectively arranged in planes so that theassemblies of tubular means form partition-walls. Thus, several bundles17 of individual tubular means are assembled together to form apartition wall such as that which is schematically illustrated in FIG.2. In each of these tubular partition walls the several tubes are curvedso as to have horizontal portions extending back and forth in the mannershown in FIG. 2. Therefore, while with the embodiment of FIG. 2 thedownwardly flowing heating gas will flow transversely across thehorizontally extending portions of the several tubular means 17, in theembodiment of FIG. I the downwardly flowing heating gas will flowtransversely across the helically extending portions of the severaltubular means 5. Except for the fact that the several tubular means 17have the configurations indicated in FIG. 2 so as to form walls oftubes, the construction of FIG. 2 is identical with that of FIG. 1 andthe corresponding components are indicated with the same referencecharacters. It is of course apparent that with FIG. 2 the feedwaterinlet 15 and chamber 13 are situated at the opposite side of the housing8, but this of course is an immaterial distinction.

Both of the heat exchangers of FIGS. 1 and 2 operate in the same way,the only difference being that the embodiment of FIG. 2 is particularlysuited for a heat exchanger adapted to operate with a heating gas ofrelatively low pressure and having a rectangular or square cross sectionwhereas the heat exchanger of FIG. 1 is ofa cylindrical cross sectionand is particularly adapted for operation with high pressure gas.

Assuming now, that, for example, as a result of a defect encountered inone of the tubes of FIG. I, it is necessary to remove this one tube fromthe operations, then the defective tube will be plugged up at its inletand outlet ends so as to be rendered inoperative. The sameconsiderations will apply in an analogous manner to FIG. 2 when adefective tube thereof must be rendered inoperative. This elimination ofa defective tube from the operations will, as has already beenmentioned, influence the transfer of heat to the adjoining tubes as aresult of the fact that heat is no longer extracted in the inoperative,defective tube, so that more heat must be extracted by the adjoiningtubes. Therefore, in accordance with the invention, the tubes in theimmediate vicinity of the inoperative tube, for example the operatingtubes of the cylinders I, 2, and 3 in the case where a tube of thecylinder 2 has been rendered inoperative, have the amount of mediumflowing therethrough increased either absolutely or relatively withrespect to the tubes in the cylinder 4, in this particular example.Thus, the throttling apertures of a throttling means at the inlet endsof the several tubular means will respectively have diameters which areenlarged at the inlet ends of the tubular means in the immediatevicinity of the inoperative tubular means either absolutely orrelatively with respect to the diameters of the plurality of tubularmeans relatively distant from the inoperative tubular means.

In the case of bundles of tubes across which the heating gas flows, suchas straight tubular portions in tube walls such as those shown in FIG. 2or in involute bundles of tubes, or in the case where there is primarilytransverse flow of the heating medium across the tubes, as in the caseof the helical tubes 5, the relative and/or absolute reduction in theextent of throttling at the inlet ends takes place at allof the tubeswhich are situated directly behind the inoperative tube in the directionof flow of the heating gas, so that in the case where a tube of the tubecylinder 2 is rendered inoperative, for example, allof the remainingtubes of the cylinder 2 will have the flow of heating mediumtherethrough throttled to a lesser extent than all of the other tubes ofthe assembly. Thus, a particular wall of tubes 17 which has one of itstubes rendered inoperative will have the flow of heating medium throughthe remaining tubes of this wall throttled to an extent less thanthrough the tubes of all of the other walls. Thus, within the same tubecylinder, tube wall, or series of involute tubes, all of the remainingoperative tubes will have the flow of heating medium therethroughthrottled to an extent less than in all of the other tubes of the entireassembly However, the immediately adjacent tubes, whether in a pair ofimmediately adjacent tube walls 17 or immediately adjacent involute orhelical tubes will also be throttled to a lesser extent, but the extentof throttling in such immediately adjacent tubes will be somewhatgreater than those tubes which remain in the same cylinder or wall.Thus, in the above example where a tube of the cylinder 2 has beenrendered inoperative, the tubes of the cylinders I and 3 will bethrottled to a lesser extent than the tubes of the cylinder 4 but agreater extent than'the'remaining operative tubes ofthe cylinder 2. j

The change in the operation of the heat exchanger to achieve the properamounts of heated medium respectively flowing through the severaltubular means to provide uniform discharge enthalpies is brought aboutby way of a throttling means situated at the inlet ends of the severaltubular means, this throttling means being omitted from FIGS. 1 and 2for the sake of clarity. In order to facilitate the construction of theheat exchanger and in order to have available the possibility ofsubsequent adaptation of the heat exchanger to the actual conditionswhich are subsequently encountered after the assembly is initiallybuilt, it has proved to be highly desirable to assemble together theinlet ends of the several tubular means of the heat exchangerfluidtightly within the bores of an inlet plate such as the inlet plate11 indicated schematically in FIGS.-l and 2 and shown schematically atan enlarged scale in section in FIGS. 3 and 4. The same considerationsapply to the case where there are a larger number of supply chambers forthe heat exchanger. The throttling means, according to one embodiment ofthe invention, takes the form of an apertured plate situated in front ofthe inlet plate 11. A change in the structure subsequent to the buildingand operation thereof can then be fully carried out by providing severalapertured plates having different arrangements and sizes of aperturestherein, so that by exchanging one apertured plate for another it ispossible to adjust the operations. A sealing means is provided toachieve a fluidtight connection between such an apertured throttlingplate and the inlet plate 11, and this sealing means preferably takesthe form of precisely flat ground surfaces of the throttling plate andinlet plate 11 directly engaging each other to form a fluidtightlysealed interface therebetween. An

' additional seal is achieved because of the differential pressureexisting before and after the apertured plate which forms the throttlingmeans. In some cases, a seal can be omitted. In this latter event theorifices of the apertured plate are dimensioned in such a way that theamount of medium flowing through the orifices together with leakagelosses between the orifices provides the right amount of medium.

Referring to FIG. 3, the feedwater inlet region of the heat exchanger isshown in detail. In this embodiment the throttling means takes the formof the apertured plate 19 provided with the throttling orifices 20. Theinlet extensions 9 of the several tubular means which form the inletends thereof are welded into the bores of the feedwater inlet plate 11.The apertured plate 19 with its orifices 20 is bolted to the inlet plateII. To improve the seal the surfaces of plates 11 and 19 which engageeach other are ground at their interface.

In the case of FIG. 4, the illustrated embodiment has a throttling meansin the form of individual throttling nozzles 21 threaded directly intothe bores of the inlet plate 11. Where the extensions 9 extend all theway to the upstream end face of the plate 11, the nozzles 21 can bethreaded directly into the extensions 9, respectively.

Whenit has been determined that the outlet enthalpies or the dischargetemperatures of the heated medium at the outlet ends of the severaltubular means deviate from the desired uniformity, the throttling meanseither in the form of the individual nozzles of FIG.-4 or aperturedplate of FIG. 3 is made in a precalculated manner so that approximatelyidentical discharge conditions will be achieved at the several outletends of the individual tubes or strings of tubes. In general, thedeviation from uniform outlet temperatures will be determined bymeasuring the outlet temperatures of the heated medium at the outletends of the individual tubes. After these outlet temperatures aremeasured it is possible in a known way to estimate the throttlingrequired for the individual tubes or the extent of throttling can benewly calculated. Under certain circumstances, however, it is desirableto carry out an estimate of the required throttling structure. Then thethrottling structure constructed as estimated is used and the dischargetemperatures are measured. If required, the estimated throttlingstructures is changed a second time for a new throttling structure whichwill give the required uniform discharge temperatures. Thus, anempirical trial-and-error method may be used.

Referring now to FIG. 5, the live-steam collector is illustratedtherein. With the construction shown in FIG. 5 it is possible to measurethe temperature of the steam at the outlet ends of the severalindividual tubular means, respectively, upon discharge of the steam intothe: collecting chamber. The live-steam tube extensions 10 of theseveral tubular means are fluidtightly welded, for example, to theoutlet plate I2 in bores of the latter, respectively, the welding beinglocated at the interior of the bores of the outlet plate, 12. Anauxiliary plate 22 is bolted to the outer, downstream end face of theoutlet plate 12, and this auxiliary plate 22 is formed with openingsrespectively forming extensions of the bores of the plate 12. Aplurality of relatively short tubes 23 are fixed, as by welding, to theauxiliary plate 22 in a manner where these several short tubes 23respectively form coaxial extensions of the extensions 10. Moreover, theinner diameters of the short tubes 23 are respectively equal to theinner diameters of the bores of the outlet plate 12. The temperaturemeasuring means takes the form of a plurality of thermocouple means 24in the form thermocouple elements situated in suitable openings formedin the short tubes 23, and these thermocouple means 24 are capable ofmeasuring the temperature of the discharging live steam in a well-knownmanner. The several thermocouple means include the thermocouple cablesor conductors 26 which are shielded from live steam by way ofarelatively large boxlike shielding sleeve 25 which is bolted to theauxiliary plate 22 in the manner shown schematically in FIG. 5. In thisway the sleeve 25 forms a protecting means to protect the conductors 26from the heated medium.

In the embodiment of FIG. 6 a different construction of a live-steamcollector 14 is illustrated. In this case the live-steam tubularextensions 10 are respectively welded in the bores of the outlet plate12 by way of welding rods. Thus, while with FIG. the welding of theextremities of the tubes to the outlet plate 12 is carried out in theinterior of the bores of the latter, in the case of FIG. 6 the weldingof the tubes 10 takes place at the downstream end face of the outletplate 12, and with the embodiment of FIG. 6 the auxiliary plate 22 isspaced slightly from the plate 12. The collecting chamber 14 for thelive steam is defined by a wall means which includes a removable covershown at the top of FIG. 6, and the auxiliary plate 12 is fixed to thisremovable cover by way of suitable bolts. As was the case with theembodiment of FIG. 5, the auxiliary plate 22 of FIG. 6 carries therelatively short tubes 23 which respectively form coaxial extensions ofthe extensions 10 and which carry the several thermocouple means 24. Theconductors 26 of the thermocouple means in the embodiment of FIG. 6 arerespectively guided through the interiors of protective tubes 27 alongthe bolts 28 which interconnect the plate 22 with the removable cover,so that in this case it is the tubes 27 which form the means forprotecting the conductors 26 from the live steam. Further shielding ofthe conductors can be provided by way of a top shielding sheet 29carried by the several connecting bolts 28 and formed withopeningsreceiving the upper open ends of the shielding tubes 27 in the mannershown in FIG. 6.

Thus, with the constructions of FIGS. 5 and 6 the measurement of thelivesteam temperature is carried out at each individual tubular means,whether this tubular means is in the form of a single tube or a group oftubes, after the heated medium has passed through the outlet plate 12.The thermocouple means used to measure the temperature can be arrangedin the path of gas flow or at the exterior of the heat exchanging tubes,in particular at the extensions 10 thereof.

The invention described above is of course not limited to use with steamgenerators. It can be used with heat exchangers such as, for example,those which use liquid metal for heat exchange or with regenerators inMHD circuits. Also, the invention is not limited to bundles of tubesarranged so that the heating gas flows directly across or primarilyacross the tubes. The invention also can be used in installations wherethe heating gas flows longitudinally along the heating tubes. In thislatter case the method and apparatus of the invention are such that thetubes which immediately surround the tube which is rendered inoperativereceive the larger amounts of the medium which is to be heated while theremaining tubes which are situated more distant from the inoperativetube receive the heated medium also in larger amounts but to a lesserextent than those tubes which immediately surround the inoperative tube.

It is apparent that when no steps are taken to compensate for an areawhere a tube or group of tubes are inoperative, the operating tubes inthe immediate vicinity of such an area will be heated to a far greaterextent that other tubes because of the greater amount of heat availableat this particular area resulting from the failure of the nonoperatingtubes to absorb their share of the heat. With the invention, because theextent of throttling in the tubes in the immediate vicinity of thenonoperating tubes is less than the throttling in tubes distant from thenonoperating tubes, a greater amount of heated medium flows through thetubes with the lesser throttling, thus reducing any tendency foroverheating in the walls of the tubes in the immediate vicinity of thenonoperating tubes.

We claim:

I. In a method for increasing the uniformity in the transfer of heat ina heat exchanger having a plurality of tubular means through which theheated medium flows, said plurality of tubular means respectively havinginlet ends and opposed outlet ends, the steps of respectively directingthe medium which is to be heated through said plurality of tubular meansfrom said inlet toward said outlet ends thereof, measuring thetemperature of the medium at the outlet end of each of said plurality oftubular means, and then providing at the inlet end of each of saidplurality of tubular means a nonadjustable throttle. to throttle saidplurality of tubular means to extents, respectively, which will achievesubstantially uniform temperatures of the heated medium at the outletends of said plurality oftubular means.

2. In a method as recited in claim 1 and wherein the amount of mediumdirected into the plurality of tubular means together with leakagelosses determine the amount of medium required to flow through theplurality of tubular means.

3. In a method as recited in claim 1 and wherein said plurality oftubular means are respectively in the form of individual tubes, and saidmeasurement of temperature respectively taking place at the outlet endsof the plurality of individual tubes.

4. In a method as recited in claim 1 and wherein the heated medium iswater, the step of converting the heated water into steam within theplurality of tubular means without any intermediate collection of theheated medium and then superheating the resulting steam.

5. In a method as recited in claim 1 and wherein ifa part of saidtubular means is no longer operative, the extent of throttling in thosetubular means immediately adjacent the part thereof which is notoperative is reduced so as to be less than the extent of throttling inthose tubular means which are more distant from the part which is notoperative, to reduce the tendency of overheating in the walls of thosetubular means adjacent the part which is not operative.

6. In a heat exchanger, a plurality of tubular means through whichmedium to be heated flows, said plurality of tubular means respectivelyhaving inlet ends and opposed outlet ends. and throttling means situatedat said inlet ends of said plurality of tubular means for throttling theflow of medium through the plurality of tubular means to an extent whichwill provide at the outlet ends of the plurality of tubular meanssubstantially uniform temperatures the degree of uniformity of which isbeyond that which would prevail without said throttling means, and aplurality of thermocouple means situated at and respectively coactingwith said outlet ends of said plurality of tubular means for measuringthe temperature of the medium discharging through the latter outletends, said throttling means having a construction selected in accordancewith the temperatures .measured by the plurality of thermocouple meansfor achieving said degree of uniformity in the temperatures of theheated medium at the outlet ends of said plurality of tubular means.

7. The combination of claim 6 and wherein an inlet plate is formed withbores respectively receiving the inlet ends of the plurality of tubularmeans, and said throttling means including an apertured plate situatedin front of said inlet plate and formed with a plurality of throttlingapertures respectively communicating with the inlet ends of theplurality of tubular means.

8. The combination of claim 7 and wherein a sealing means is situatedbetween said plates for providing a fluidtight coaction therebetween.

9. The combination of claim 8 and wherein said sealing means includesflat-ground surfaces of said plates which engage each other and form afluidtight interface therebetween.

10. The combination of claim 6 and wherein an outlet plate is formedwith bores respectively receiving the outlet ends of the plurality oftubular means, and a plurality of relatively short tubes respectivelycommunicating with said outlet ends of said plurality of tubular meansand at which said plurality of thermocouple means are respectivelylocated.

11. The combination of claim 10 and wherein an auxiliary plate carriessaid tubes and fluidtightly engages said outlet plate while providingcommunication between said tubes and said outlet ends of said pluralityof tubular means, respectively.

12. The combination of claim 10 and wherein a chamber means communicateswith said outlet ends for receiving the medium discharging therefrom,said chamber means having a removable cover, and connecting meansconnecting said tubes tors extending through said wall means andprotecting means coacting with said conductors for protecting the latterfrom the heated medium discharging from said outlet ends of saidplurality of tubular means.

1. In a method for increasing the uniformity in the transfer of heat ina heat exchanger having a plurality of tubular means through which theheated medium flows, said plurality of tubular means respectively havinginlet ends and opposed outlet ends, the steps of respectively directingthe medium which is to be heated through said plurality of tubular meansfrom said inlet toward said outlet ends thereof, measuring thetemperature of the medium at the outlet end of each of said plurality oftubular means, and then providing at the inlet end of each of saidplurality of tubular means a nonadjustable throttle, to throttle saidplurality of tubular means to extents, respectively, which will achievesubstantially uniform temperatures of the heated medium at the outletends of said plurality of tubular means.
 2. In a method as recited inclaim 1 and wherein the amount of medium directed into the plurality oftubular means together with leakage losses determine the amount ofmedium required to flow through the plurality of tubular means.
 3. In amethod as recited in claim 1 and wherein said plurality of tubular meansare respectively in the form of individual tubes, and said measurementof temperature respectively taking place at the outlet ends of theplurality of individual tubes.
 4. In a method as recited in claim 1 andwherein the heated medium is water, the step of converting the heatedwater into steam within the plurality of tubular means without anyintermediate collection of the heated medium and then superheating theresulting steam.
 5. In a method as recited in claim 1 and wherein if apart of said tubulAr means is no longer operative, the extent ofthrottling in those tubular means immediately adjacent the part thereofwhich is not operative is reduced so as to be less than the extent ofthrottling in those tubular means which are more distant from the partwhich is not operative, to reduce the tendency of overheating in thewalls of those tubular means adjacent the part which is not operative.6. In a heat exchanger, a plurality of tubular means through whichmedium to be heated flows, said plurality of tubular means respectivelyhaving inlet ends and opposed outlet ends, and throttling means situatedat said inlet ends of said plurality of tubular means for throttling theflow of medium through the plurality of tubular means to an extent whichwill provide at the outlet ends of the plurality of tubular meanssubstantially uniform temperatures the degree of uniformity of which isbeyond that which would prevail without said throttling means, and aplurality of thermocouple means situated at and respectively coactingwith said outlet ends of said plurality of tubular means for measuringthe temperature of the medium discharging through the latter outletends, said throttling means having a construction selected in accordancewith the temperatures measured by the plurality of thermocouple meansfor achieving said degree of uniformity in the temperatures of theheated medium at the outlet ends of said plurality of tubular means. 7.The combination of claim 6 and wherein an inlet plate is formed withbores respectively receiving the inlet ends of the plurality of tubularmeans, and said throttling means including an apertured plate situatedin front of said inlet plate and formed with a plurality of throttlingapertures respectively communicating with the inlet ends of theplurality of tubular means.
 8. The combination of claim 7 and wherein asealing means is situated between said plates for providing a fluidtightcoaction therebetween.
 9. The combination of claim 8 and wherein saidsealing means includes flat-ground surfaces of said plates which engageeach other and form a fluidtight interface therebetween.
 10. Thecombination of claim 6 and wherein an outlet plate is formed with boresrespectively receiving the outlet ends of the plurality of tubularmeans, and a plurality of relatively short tubes respectivelycommunicating with said outlet ends of said plurality of tubular meansand at which said plurality of thermocouple means are respectivelylocated.
 11. The combination of claim 10 and wherein an auxiliary platecarries said tubes and fluidtightly engages said outlet plate whileproviding communication between said tubes and said outlet ends of saidplurality of tubular means, respectively.
 12. The combination of claim10 and wherein a chamber means communicates with said outlet ends forreceiving the medium discharging therefrom, said chamber means having aremovable cover, and connecting means connecting said tubes to saidcover for removal of said tubes and plurality of thermocouple means withsaid cover.
 13. The combination of claim 10 and wherein a wall meansdefines a chamber receiving the medium discharging through said outletends, said thermocouple means including conductors extending throughsaid wall means and protecting means coacting with said conductors forprotecting the latter from the heated medium discharging from saidoutlet ends of said plurality of tubular means.